1. Field of the Invention
The invention relates to disk drives. More particularly, the invention relates to providing pre-determined servo position correction values for use during disk drive initialization to improve track following on a reserved track of a disk.
2. Description of the Related Art
Today, computing devices such as personal computers, personal digital assistants, cell-phones, etc., are routinely used at work, at home, and everywhere in-between. Computing devices advantageously enable the use of application specific software, file sharing, the creation of electronic documents, and electronic communication and commerce through the Internet and other computer networks. Typically, each computing device has a storage peripheral such as a disk drive.
A huge market exists for disk drives for mass-market computing devices such as desktop computers and laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g. personal digital assistants (PDAs), cell-phones, digital cameras, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Disk drives typically employ a moveable head actuator to frequently access large amounts of data stored on a disk. One example of a disk drive is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the moveable transducer head over a particular track on the disk to read or write information from and to that track, respectively.
Typically, a conventional hard disk drive includes a disk having a plurality of concentric tracks. Each surface of each disk conventionally contains a plurality of concentric data tracks angularly divided into a plurality of data sectors. In addition, special servo information may be provided on each disk to determine the position of the moveable transducer head.
The most popular form of servo is called “embedded servo” wherein the servo information is written in a plurality of servo sectors that are angularly spaced from one another and are interspersed between data sectors around each track of each disk.
Each servo sector typically includes at least a track identification (TKID) field, a sector ID field having a sector ID number to identify the sector, and a group of servo bursts (e.g. an alternating pattern of magnetic transitions) which the servo control system of the disk drive samples to align the moveable transducer head with or relative to a particular track. Typically, the servo control system moves the transducer head toward a desired track during a “seek” mode using the TKID field as a control input.
Once the moveable transducer head is generally over the desired track, the servo control system uses the servo bursts to keep the moveable transducer head over that track in a “track follow” mode. During track follow mode, the moveable transducer head repeatedly reads the sector ID field of each successive servo sector to obtain the binary encoded sector ID number that identifies each sector of the track. In this way, the servo control system continuously knows where the moveable transducer head is relative to the disk. Further, position error signals (PESs) are often utilized as a feedback signal for the servo control system during track following operations. The PES signal may be derived from read servo bursts as the head flies over the servo bursts of the servo sectors of the disk. The PES signal may be utilized by the servo control system to keep the head near the center of the track.
As disk drive manufacturers have been forced to increase data capacity in disk drives to remain competitive, a greater number of tracks are now provided on each disk for data storage. In order to accomplish this, the width of the tracks have been made increasingly smaller and the servo bursts used to maintain track following operations are now increasingly spaced closer and closer together. Consequently, servo control margins for track following have likewise become increasingly more stringent and more sensitive to error.
With increasingly narrower tracks and tighter servo control margins, one area of concern arises during disk drive initialization and power-up. As is well known, in many of today's disk drives, diagnostic and calibration functions are performed during initialization and power-up with the aid of specialized reserved tracks. Typically, reserved tracks are located at the outer diameter of a disk of a disk drive. However, reserved tracks may also be located at the inner diameter of the disk. Reserved tracks may be utilized by the servo control system of the disk drive during calibration.
Although position linearity compensation is sometimes used in track following in disk drives, disk drives presently do not employ position linearity compensation when track following on the reserved track to read calibration data and initialize the disk drive. Further, although disk drives may create a calibrated compensation table during the calibration process for the disk drive, due to the increasingly stringent servo control margins resulting from narrower tracks and more closely spaced servo bursts, off-track gain variations may occur that prevent the disk drive from effectively track-following on the reserved track to read any calibrated linearity compensation parameters for the servo system, thereby detrimentally affecting the initialization process and even causing disk drive failure.